Surface Molecule Manipulated Pt/TiO2 Catalysts for Selective Hydrogenation of Cinnamaldehyde

<p>Surface states—the electronic states emerging as a solid material terminates at a surface—are usually vulnerable to contaminations and defects. This fundamental limitation has prohibited systematic studies of the potential role of surface states in surface reactions and catalysis, especially in more realistic environments. Herein, we use selective hydrogenation of <a>cinnamaldehyde</a> (CAL) on <a>platinum-covered titanium oxide</a> (Pt@P25) as a prototype reaction, and show that the competitive exchange of extra-introduced species (sodium hydroxide and sodium formate) with spontaneously formed weak bound carbonate and bicarbonate anions at Pt NPs can reconstruct the surface states, which directs the preferred adsorption of the conjugated C=O and C=C double bonds of CAL, and consequently, results in highly efficient synthesis of unsaturated alcohol cinnamyl alcohol (COL) and saturated aldehyde hydrocinnamaldehyde (HCAL) with high selectivity of 98.9% and 99.5%, respectively. Our concept of restructured surface states to tune the chemoselectivity of α, β-unsaturated aldehydes triggered by the selective adsorption of alien molecules may lead to new design principles of heterogeneous catalysts, beyond the conventional d-band theory.</p>

Surface Molecule Manipulated Pt/TiO2 Catalysts for Selective Hydrogenation of Cinnamaldehyde

<p>Surface states—the electronic states emerging as a solid material terminates at a surface—are usually vulnerable to contaminations and defects. This fundamental limitation has prohibited systematic studies of the potential role of surface states in surface reactions and catalysis, especially in more realistic environments. Herein, we use selective hydrogenation of <a>cinnamaldehyde</a> (CAL) on <a>platinum-covered titanium oxide</a> (Pt@P25) as a prototype reaction, and show that the competitive exchange of extra-introduced species (sodium hydroxide and sodium formate) with spontaneously formed weak bound carbonate and bicarbonate anions at Pt NPs can reconstruct the surface states, which directs the preferred adsorption of the conjugated C=O and C=C double bonds of CAL, and consequently, results in highly efficient synthesis of unsaturated alcohol cinnamyl alcohol (COL) and saturated aldehyde hydrocinnamaldehyde (HCAL) with high selectivity of 98.9% and 99.5%, respectively. Our concept of restructured surface states to tune the chemoselectivity of α, β-unsaturated aldehydes triggered by the selective adsorption of alien molecules may lead to new design principles of heterogeneous catalysts, beyond the conventional d-band theory.</p>

Surface Molecule Manipulated Pt/TiO2 Catalysts for Selective Hydrogenation of Cinnamaldehyde

<p>Surface states—the electronic states emerging as a solid material terminates at a surface—are usually vulnerable to contaminations and defects. This fundamental limitation has prohibited systematic studies of the potential role of surface states in surface reactions and catalysis, especially in more realistic environments. Herein, we use selective hydrogenation of <a>cinnamaldehyde</a> (CAL) on <a>platinum-covered titanium oxide</a> (Pt@P25) as a prototype reaction, and show that the competitive exchange of extra-introduced species (sodium hydroxide and sodium formate) with spontaneously formed weak bound carbonate and bicarbonate anions at Pt NPs can reconstruct the surface states, which directs the preferred adsorption of the conjugated C=O and C=C double bonds of CAL, and consequently, results in highly efficient synthesis of unsaturated alcohol cinnamyl alcohol (COL) and saturated aldehyde hydrocinnamaldehyde (HCAL) with high selectivity of 98.9% and 99.5%, respectively. Our concept of restructured surface states to tune the chemoselectivity of α, β-unsaturated aldehydes triggered by the selective adsorption of alien molecules may lead to new design principles of heterogeneous catalysts, beyond the conventional d-band theory.</p>

Heck Transformations of Biological Compounds Catalyzed by Phosphine-Free Palladium

The development and optimization of synthetic methods leading to functionalized biologically active compounds is described. Two alternative pathways based on Heck-type reactions, employing iodobenzene or phenylboronic acid, were elaborated for the arylation of eugenol and estragole. Cinnamyl alcohol was efficiently transformed to saturated arylated aldehydes in reaction with iodobenzene using the tandem arylation/isomerization sequential process. The arylation of cinnamyl alcohol with phenylboronic acid mainly gave unsaturated alcohol, while the yield of saturated aldehyde was much lower. Catalytic reactions were carried out using simple, phosphine-free palladium precursors and water as a cosolvent, following green chemistry rules as much as possible.

Enantioselective Construction of Alkylated Centers: The Rawal Synthesis of (+)-Fornicin C

Kazuaki Kudo of the University of Tokyo showed (Angew. Chem. Int. Ed. 2013, 52, 11585) that the dienyl aldehyde 1 could be reduced to the saturated aldehyde 2 with high ee. Alexandre Alexakis of the University of Geneva effected (Angew. Chem. Int. Ed. 2013, 52, 12701) conjugate addition to the unsaturated amide 3 to give 4 in high ee. Professor Alexakis also carried out (Chem. Eur. J. 2013, 19, 11352) enantioselective conjugate addition to the alkynyl nitro alkene 5, leading to 6. Gerrit J. Poelarends of the University of Groningen found (Chem. Eur. J. 2013, 19, 14407) that the enzyme 4-oxalocrotonate tautomerase mediated the conjugate addition of acetaldehyde to a nitroalkene 7 to deliver the aldehyde 8 in high ee. Tohru Yamada of Keio University developed (Chem. Commun. 2013, 49, 8371) an enantioselective Cu catalyst for the Claisen rearrangement of 9 to 10. Shi-Kai Tian of USTC Hefei made (Chem. Commun. 2013, 49, 8190) the primary amine of 11 a leaving group, coupling 11 with 12 to make 13. David W. C. MacMillan of Princeton University alkylated (J. Am. Chem. Soc. 2013, 135, 11756) the aldehyde 14 with the boronic acid 15, to give 16 in high ee. Paolo Melchiorre of ICIQ Tarragona effected (Nature Chem. 2013, 5, 750) the enantioselective construction of the quaternary cen­ter of 19 by alkylation of the aldehyde 17 with 18. Other methods for the enantioselective construction of quaternary alkylated cen­ters have also been put forward. Varinder K. Aggarwal of the University of Bristol elaborated (J. Am. Chem. Soc. 2013, 135, 16054) the inexpensive secondary ester 20 into the alkylated product 21. Jianwei Sun of the Hong Kong University of Science and Technology cyclized (Angew. Chem. Int. Ed. 2013, 52, 13593) the prochiral diol 22 to 23 in high ee. Amir H. Hoveyda of Boston College effected (Angew. Chem. Int. Ed. 2013, 52, 8156) enantioselective conjugate addition to the enone 24 to give 25. Xiaoming Feng of Sichuan University devised (Angew. Chem. Int. Ed. 2013, 52, 10883) a catalyst for the addition of the bulky α-diazo ester 26 into the α-keto ester 27, leading to 28.

Best Synthetic Methods: Functional Group Transformations

Vinyl glycine 2 is a useful precursor to a variety of amino acids. Timothy E. Long of the University of Georgia found (Tetrahedron Lett. 2009, 50, 5067) that the o-nitrophenyl sulfoxide 1 eliminated smoothly in refluxing toluene. Alicia Boto and Rosendo Hernández of IPNA La Laguna observed (Tetrahedron Lett. 2009, 50, 3974) that a related selenoxide elimination proceeded to give the single regioisomer 4. Avelino Corma of the Universidad Politécnica de Valencia developed ( Chemical Commun. 2009, 4947) a gold catalyst for the selective hydroboration of alkynes over alkenes. Eiji Shirakawa and Tamio Hayashi of Kyoto University devised (Chemical Commun. 2009, 5088) a Ru catalyst for the conversion of an alkenyl triflate such as 8 to the corresponding bromide. Tristan H. Lambert of Columbia University found (J. Am. Chem. Soc. 2009, 131, 13930) that the dichloride 11 smoothly converted a variety of alcohols into the corresponding chlorides. Crown ethers have been used to promote SN2 reactivity by solubilizing the metal cation. Sungyul Lee of Kyunghee University, Dae Yoon Chi of Sogang University, and Choong Eui Song of Sungkyunkwan University demonstrated (Angew. Chem. Int. Ed. 2009, 48, 7683) that the inexpensive polyethylene glycols were also effective. Mugio Nishizawa of Tokushima Bunri University devised (Synlett 2009, 1175) conditions for the rapid regioselective hydration of hydroxy alkynes such as 15. Jaume Vilarrasa of the Universitat de Barcelona developed (Organic Lett. 2009, 11, 4414) a mild alternative protocol for the Nef reaction, converting a nitroalkane such as 17 into the corresponding ketone under neutral conditions. Clément Mazet of the University of Geneva optimized (Tetrahedron Lett. 2009, 50, 4141) the Ir-catalyzed conversion of an allylic alcohol 19 into the saturated aldehyde. Jonathan M. J. Williams of the University of Bath established (Angew. Chem. Int. Ed. 2009, 48, 7375) that under Ir-catalyzed “borrowing hydrogen” conditions, alkyl amines could donate alkyl groups to anilines such as 21. Danfeng Huang and Yulai Hu of Northwest Normal University devised (Organic Lett. 2009, 11, 4474) a simple protocol for conversion of an acid 23 to the Weinreb amide 24. of the Universitat

Transfer Hydrogenation of Carbonyl Compounds and Alkenes Catalyzed by Ruthenium(II)-N-Heterocycle Carbene Complexes

The Ru(II)-N-heterocycle carbene complexes [RuCl2(η6-p-cymene)L] (L = 1-butyl-3-methylimid- azol-2-ylidene) and [RuCl(η6-p-cymene)L(pta)]Cl (pta = 1,3,5-triaza-7-phosphaadamantane) showed excellent catalytic activities (with turnover frequencies up to 1116 h-1) in the hydrogen transfer reduction of cinnamaldehyde and several ketones using propan-2-ol/KOH as a H-donor. Similar hydrogenations of trans-stilbene and cyclohexene were characterized by low conversions. The hydrogenation of 4-phenylbut-3-en-2-one and cinnamaldehyde proceeded with moderate selectivities of the formation of the saturated alcohol or of the of C=C hydrogenation (giving saturated ketone or saturated aldehyde). In the case of cinnamaldehyde, the unsaturated alcohol is initially formed; however, subsequent redox isomerization to the saturated aldehyde with the same catalyst diminishes its yield. The hydrogen transfer from formate to 4-phenylbut-3-en-2-one in an aqueous-organic two-phase mixture was also demonstrated.